[Nop head] discovered that cheap multimeter leads costing only a few bucks can come with more than one may have bargained for. The first set had a large amount of useful-looking attachments, but the wires used for the leads were steel with a resistance of about one ohm each. With two leads in use, that means any resistance measurement gets two ohms added for free. More seriously, when measuring current, the wires can heat up rapidly. Voltage measurements would be affected the least, but the attachments and lead design expose a large amount of bare metal, which invites accidental shorts and can be a safety hazard with higher voltages.
Are all cheap multimeter leads similarly useless? Not necessarily. [nop head] also purchased the set pictured here. It has no attachments, but was a much better design and had a resistance of only 64 milliohms. Not great, but certainly serviceable and clearly a much better value than the other set.
It’s usually not possible to identify garbage before it’s purchased, but [nop head] reminds us that if you do end up with trash in hand, poor quality counterfeits can be good for a refund. That goes for electronic components, too.
Thank you Captain Obvious !
Steel wires? That’d be just brilliant for AC… The skin effect would quickly increase the resistance.
It won’t make much of a difference as the bandwidth of your multimeter will be the limit. I would be surprise if your average DMM have bandwidth anywhere near 100kHz.
You’ll need much higher frequency before it becomes an issue.
the skin depth for steel at 100kHz is only ~25um
https://www.eevblog.com/forum/testgear/multimeter-bandwidth/
>From what I can tell, here’s the bandwidths of 3 nice $100 class meters
>BK Precision BK2709B 500Hz
>Amprobe AM270 20KHz
>Brymen BM257 400Hz (per Lightages correction, thanks)
>In the $100 USD range, you can buy an used Fluke 87 (original) series I and it has a 20kHz as well with the usual qualifications as per
Also consider the fact that the DMM input impedance is very high, so a bit of skin effects in series isn’t going to be an issue.
So today’s lesson is free isn’t free? *deletes Linux* :-D
rm – Remove in Linux
DOS has del – delete and earse
No problem, just use Windows to delete Linux.
E arse now that’s a command!
e-arse as in e-mail…
I have some Fluke branded leads that are shithouse as well they come in at 14.5ohms total! And I didn’t buy them off eBay
BTW I bought two probes (different times) similar to the one in the bottom picture. One has thin non-plated wires (very high resistance) and will and poor banana plugs. I found a “20A” version from a different store. That one is similar to OP’s 64 milliohms probe and seem to have better banana plugs.
The Fluke probes I had was poorly made. The wire from the plug side came off as they loosely crimped it. The wires have been oozing some green liquid over time. Probably plastic wires insulation leeching and attacks the copper wires. That’s why I turned to chinese probes in the first place. The alternative would be buying probes, shrouded plugs and proper wires but they cost 10-20x.
How cheap is the multimiter that cheap leads are used?
I still use a multimeter I bought in the late 90s for $10 from Ace Hardware. I see it all the time on Youtube channels (e.g. BigClive) as the cheap shitty multimeter they bought off ebay. I’m curious how different mine is from theirs and which is better.
Did the march of time reduce the cost of components so internally newer ones or better or did building to a price point get in the way?
The cover picture shows the pretty much precisely the first (and for a long time only) set of testing leads that I had. Made me pretty happy for a long time when I was a kid and I still must have them around (bananaaligator was eventually my favourite configuration) connected to some power supply. Sad (though not surprising) to read that they are not perfect. I will still keep them in good memories. ;)
Since I don’t get in to anything hotter than 220, and that’s rare. My leads are line cord soldered to a combo pointy end probe and alligator red and alligator only for the black lead. At the other end are old school bananas no booties. Just naked bananas. Always reads less than .4 Ohm.
What really gets me for cheapness and high resistance is those bend the wire over on to the plastic insulation and crimp the whole end into alligator clip leads, worthless! I think some of this dumbness goes on in the test leads too, it just gets molded over with plastic.
If I can’t take apart and inspect it I take it to the trash can.
Use that for measuring several amps of current (eg in a 16 amp circuit) and you have a fire.
Actually, I bought a bunch of “the ones pictured here” in China, and they are also hit and miss.
I sold an insulation tester that I bought for £1 in the car boot sale and which needed fixing + a set of cables, and it would work fine with one set, but refused to work with another set. Even thought the sets looked the same, they were bought from different sellers.
When I resold a bench multimeter, I also kept the ISO-Tech ones (not great, but still decent) and threw in the new Chinese set with the highest resistance. In my defence, the buyer haggled the price ;)
I just checked all my cables on my Fluke 79 (not calibrated, but at least the delta should be ok):
– Fluke set (scavenged from a Fluke clampmeter I resold with Chinese cables), 1000V CAT3: 0.3 ohm
– ISO tech set, 1500V CAT?: 0.2 ohm
– Chinese “Victor” branded, allegedly 1000V CAT3: 0.3 ohm
– Identical Victor Chinese set: 0.3 ohm
These 2 Chinese sets are identical Victor branded, but as I said, I had some other sets that looked the same, allegedly 1000V CAT3, not Victor branded, and they had a much higher resistance. As mentioned earlier, the Robin insulation tester wouldn’t pass its self test with one of those sets, and I eventually offloaded them with another multimeter at some point.
I also gave a bunch of these chinese ones to my dad, but for what he does, they are good enough. He also breaks them quick: if you apply a lot of pressure on the probes, the plastic will snap between the grey bit at the tip and the coloured body. I don’t know if the Victor ones do the same, I’m not sure what I gave my dad anymore.
there’s yet no mention of the zero-adjustment for an ohmmeter?
Hey, it’s last June again!
Selling your manufacturing soul to China has consequences.
It might be the multimeter range switch contacts, not always leads.
Lord. Most of the time this amounts to a small fraction of your reading. Here is an idea. If you need accurate readings, don’t use low end test equipment. For me, the vast majority of the time I am happy with the 3.5 digit dvm’s that HF gives out. Hell, I don’t even change the batteries. When one croaks I just grab another off the shelf. If I drop it, or step on it, or slam in in the car door, I don’t feel too bad about it. It is actually pretty rare that I need a more refined device, and I save them for when I do really need them. BTW, if you are going to be taking sub ohm readings you really should be using a 4 wire ohmmeter anyway.